The invention relates to a pipe cleaning apparatus for oil and gas pipelines having deposits for example in the form of paraffins, which apparatus is pushed through the pipeline by a liquid flow for cleaning purposes, with the apparatus having a shield that forms one or more apertures for a passing liquid flow in order to form a predetermined flow resistance in the pipeline, wherein the shield is coupled to a braking device and can have a cleaning apparatus on its front side.
Depending on the forwarding region, solids and viscous products such as for example paraffins tend to deposit on the walls of oil and gas pipelines. Pipes of this kind clog up particularly rapidly when they are laid in cold surroundings such as for example at the bottom of the sea for offshore forwarding. In a case of this kind an attempt is presently being made to cleanse the pipes mechanically with a pipe cleaning device which is moved along by the pipe flow as long as they are not completely clogged. This type of pipe cleaning, or "pigging", is solved only incompletely, since it must be used over long distances, i.e. over several miles. The devices often get stuck in the deposits and the cleaning head fails to function. The only remedy is then to cut out sections of pipes and clean them with drill rods, which is an extremely costly endeavor for pipelines that are laid on the ocean floor, considering that the sections of pipe must be welded together again after cleaning.
Oil companies and suppliers are thus attempting to develop pipe cleaning apparatuses which can be transported along by a liquid flow over long distances without cable or pipe connections of any kind, where the liquid flow can be opposed by a pressure of 40 to 60 bar. Thus a brochure of GIRARD INDUSTRIES INC., 6531 North Eldridge Pkwy, Houston, Tex. 77041-3507 from the year 1994 shows so-called "cleaning pigs" which consist of two plate-like plastic disks between which cleaning brushes pressing radially outwards are mounted on a connecting piece. The entire structure is moved forward by a liquid flow in the pipe to be cleaned, and some embodiments can also be moved in both directions. The plate-like disks push and pull the brushes lying between them in order to scrape deposits off the pipe wall. The difference in pressure ahead of and behind the "cleaning pig" depends on the flow resistance of plates and brushes as well as on the friction of the plates and brushes against the pipe wall. Similar arrangements are offered by GIRARD in a brochure copyrighted 1988 as "F. H. Maloney Spring Loaded Pipeline Cleaning Pigs".
A similar device is proposed by the Shell Oil Company in U.S. patent application Ser. No. 08/396,807 of Mar. 2, 1995, now abandoned. The device consists of a sealing body on which a rotatably journalled cleaning head with nozzles is mounted in the direction of flow in order to remove solids, such as wax for example, from the pipe wall. A braking device is secured to the sealing body and has brake shoes which press radially against the pipe wall in order to thus brake the movement of the sealing body in the flow of the pipe and to build up a pressure difference. This pressure difference is used to provide the nozzles with a liquid jet via internal bypass lines and to set the cleaning head rotating.
Furthermore, the U.S. Pat. No. 4,920,600 shows a pipe cleaning apparatus which consists of a cleaning head with scrapers which broaden radially opposite to the direction of flow. The cleaning head is axially firmly secured to a carrier body which is executed as a pipe plug and has two sealing plates, each of which consists of a plurality of mutually movable elements in order to transmit pressure blows driven by the flow to the cleaning head.
A disadvantage of the devices listed here consists in the fact that they are restricted to thin encrustations and deposits, since they simply get stuck in thicker layers of deposits. Furthermore, the thickness of the deposits to be encountered cannot readily be predicted. For this reason the use of such devices is always associated with a high risk of getting stuck and incurring the cost and effort of separating out sections of pipeline.